A multiple-optical-axis photoelectric sensor used to control supply of power to a machine in a dangerous region is configured to turn off an output in order to ensure safety, when an object is detected, and when occurrence of an abnormality is detected in the sensor (for example, refer to Patent Document 1).
Some of this type of sensors are designed to allow switching of operation mode according to an installation environment, a use application, and the like. For example, in a multiple-optical-axis photoelectric sensor developed by an applicant, the operation mode for an interlock function is set by a combination of connection states of two signal lines (see Non-Patent Document 1)
FIG. 10 illustrates a wiring method disclosed in Non-Patent Document 1 regarding the operation mode of the interlock function. Here, one of an automatic reset mode and a manual reset mode is selected by a function selecting signal line P4 and a reset-signal inputting signal line P2.
The automatic reset mode provides automatic return of the sensor output to, an on-state after an optical axis is blocked to stop the output of the sensor, according to release of the light obstruction state. When the automatic reset mode is set, as illustrated in FIG. 10(1), the reset signal inputting signal line P2 is short-circuited to a 24-V (high-level) power supply line 3H through a normally-closed switch S1 while the function selecting signal line P4 is connected to the 0-V (low-level) power supply line 3L.
The manual reset mode maintains an output off-state after the light obstruction state is released and the output is returned to the on-state from input of the reset signal. When the manual reset mode is set, as illustrated in FIG. 10(2), the reset-signal inputting signal line is connected to the 24-V power supply line 3H through a normally-open switch S2, while the interlock function selecting signal line is connected to the 24-V power supply line 3H.
According to the above configuration, the automatic reset mode is set when the low-level signal is input from the signal line P4 while the high-level signal is input from the signal line P2, and the manual reset mode is set when the high-level signal is input from the signal line P4 while the low-level signal is input from the signal line P2. An error state occurs when a different combination of input signals from the two combinations described above is input.